Radio frequency identification (RFID) technology comprises a non-contact automatic identification system. RFID technology provides an automatic method for efficiently collecting product, place, time or transaction data without human intervention.
An RFID system generally comprises a reader unit that uses an antenna to transmit radio energy to interrogate a responder such as a radio frequency identification (RFID) tag. An RFID tag does not have an on-chip battery, but rather receives its energy from the incoming RF signal from the reader unit. The RFID tag uses the energy from the incoming RF signal to extract the data that is stored in the chip of the RFID tag and send the data back to the reader unit. The reader unit can then send the data from the RFID tag to a computer for further processing.
An RFID system usually comprises a reader unit and a plurality of RFID tags. An RFID system can be used to identify persons or objects that have an RFID tag and that are located within the reading range of the reader unit. Using a pre-defined communication protocol the reader unit is capable of communicating with all of the RFID tags that are located within range.
In one embodiment of an RFID system the reader unit transmits data to an RFID tag with an amplitude modulated (AM) radio frequency (RF) signal having a frequency in the range from nine hundred MegaHertz (MHz) to two and four tenths GigaHertz (2.4 GHz). In the RFID tag a demodulator recovers the baseband signal from the incoming RF signal. A demodulator in an RFID tag should be able to recover the baseband signal of an RF amplitude that has sufficient power to power the chip of the RFID tag.
The demodulator in an RFID tag should also be able to decode ASK demodulation depths from twenty percent (20%) to one hundred percent (100%). The demodulator in an RFID tag should also be able to receive data at data rates that range from sixteen thousand bits per second (16 Kbps) to eighty thousand bits per second (80 Kbps) or higher.
An RFID tag can be architecturally divided into three major blocks. As shown in FIG. 1, the three major blocks of a prior art RFID tag 100 are an analog block 110, a digital state machine block 120, and a non volatile memory (NVM) block 130. The analog block 110 comprises a demodulator circuit 140 and a modulator circuit 150. Radio frequency (RF) energy couples to the elements of the RFID tag 100 through antenna 160. On-chip direct current (DC) power is generated in RFID tag 100 using a charge pump circuit (not shown in FIG. 1). The DC power is used to power the remaining functions of the chip of RFID tag 100.
Data detection, voltage regulation, backscatter clock generation, and other functions are performed in the analog domain of analog block 110. The actual protocol functions are handled in the digital state machine block 120. EPC data or user data may be stored either in the non volatile memory (NVM) block 130 or in a laser read only memory (ROM) unit (not shown).
The functions of direct current (DC) power generation, clock signal generation, demodulation, etc. are performed using the analog circuitry in the analog block 110. The digital state machine block 120 performs the communication protocol function with the RFID reader unit (not shown).
FIG. 2 illustrates a block diagram showing how a prior art demodulator circuit 210 is connected to other portions of the integrated circuit chip of a prior art RFID tag 100. Demodulator 210 and the remaining analog and digital portions 220 of the chip operate with the power supply that is generated by a charge pump circuit 230 and regulated by a regulator circuit 240.
A demodulator circuit 210 of an RFID tag 100 has a wide range of requirements for different regions of operation. For example, the amplitude modulated (AM) signal data rate may be modulated with radio frequency (RF) power levels from minus ten decibels (−10 dBm) to positive twenty decibels (20 dBm) (i.e., from one hundred microwatts (100 μW) to one hundred milliwatts (100 mW). As previously mentioned, the amplitude modulated (AM) signal data rate can vary from sixteen thousand bits per second (16 Kbps) to eighty thousand bits per second (80 Kbps) or higher with a modulation depth that can vary from twenty percent (20%) to one hundred percent (100%). In addition, the rise and fall times of these signals can be between three tenths microsecond (0.3 μs) and ten microseconds (10 μs) depending upon the data rate.
A demodulator circuit 210 of an RFID tag 100 must also not introduce a large delay time during the demodulation process. The demodulator circuit 210 should provide the output of the demodulation process with a delay that is less than one microsecond (1.0 μs).
There is a need in the art for a system and method for providing an improved data detection circuit for radio frequency (RF) signals in radio frequency identification (RFID) tags in RFID systems. There is also a need in the art for a system and method for providing an improved demodulator circuit for use in radio frequency identification (RFID) tags in RFID systems.